1. Field of the Invention
The present invention relates generally to a hydrotreating process for converting fatty materials such as triglycerides, diglycerides, monoglycerides, and free fatty acids into hydrocarbon compounds, especially diesel fuel range hydrocarbons and propane. The propane and any other light hydrocarbons produced during the hydrotreating process are used to generate hydrogen that is recycled to the hydrotreating process thereby reducing the demand for outside hydrogen sources.
2. Description of the Prior Art
As the demand for hydrocarbon fuels increases, the incentives for developing renewable hydrocarbon sources increase as well. Various economic, environmental and political pressures are driving the development of alternative energy sources that are compatible with existing technologies and infrastructure. The development of renewable hydrocarbon fuel sources, such as plant and animal sources, has been proposed as a solution to this problem.
“Bio-Diesel” is one such product that may be produced by subjecting a base vegetable oil to a transesterification process using methanol to convert the base oil to desired methyl esters. After processing, the products have very similar combustion properties as compared to petroleum-derived hydrocarbons. However, Bio-Diesel exhibits a number of down sides, especially its poor oxidative stability, propensity to gel in cold climates, and its cost.
Unmodified vegetable oils and fats have also been used as additives in diesel fuel to lower cost and improve the lubricity of the fuel. However, problems such as injector coking and the degradation of combustion chamber conditions have been associated with these unmodified additives. Processes for converting vegetable oil into hydrocarbons have been developed. However, these processes have often involved harsh reaction conditions, or the products from the reaction exhibit undesirable properties (such as high pour and cloud points) which render them unsuitable for use in diesel fuel. Further, these processes require significant quantities of hydrogen which increases the overall cost of producing the fuel.
Therefore, a need exists for a process for converting vegetable oils and fats into hydrocarbon compounds in the diesel fuel boiling range, especially C15-C18 hydrocarbons, that requires a minimal amount of outside hydrogen. Thus, it would be advantageous if the process could internally generate a large portion, if not a majority, of the hydrogen needed to carry out the conversion of the oils and fats to hydrocarbon compounds.